This is a question that Des has pondered frequently. Carbon Counter gives us a nice analysis.

11 June 2015 (Carbon Counter) – Various scenarios have been put forward showing that 100% renewable energy is achievable. Some of them even claim that we can move completely away from fossil fuels in only couple of decades. A world entirely without fossils might be desirable, but is it achievable?

The current feasibility of 100% renewable energy is easily tested by asking a simple question. Can you build a wind turbine without fossil fuels? If the machines that will deliver 100% renewable energy cannot be made without fossil fuels, then quite obviously we cannot get 100% renewable energy.

This is what a typical wind turbine looks like:

What is it made of? Lots of steel, concrete and advanced plastic. Material requirements of a modern wind turbine have been reviewed by the United States Geological Survey. On average 1 MW of wind capacity requires 103 tonnes of stainless steel, 402 tonnes of concrete, 6.8 tonnes of fiberglass, 3 tonnes of copper and 20 tonnes of cast iron. The elegant blades are made of fiberglass, the skyscraper sized tower of steel, and the base of concrete.

These requirements can be placed in context by considering how much we would need if we were to rapidly transition to 100% wind electricity over a 20 year period. Average global electricity demand is approximately 2.6 TW, therefore we need a total of around 10 TW of wind capacity to provide this electricity. So we would need about 50 million tonnes of steel, 200 million tonnes of concrete and 1.5 million tonnes of copper each year. These numbers sound high, but current global production of these materials is more than an order of magnitude higher than these requirements. [more]